The objective of this study is to examine how the share of public transit investments affects urban structure using spatial-temporal distribution of transport passenger flows over transport network alternatives. A methodology to model urban structure (identifying and classifying centers and subcenters) based on urban travel data (interzonal urban passenger flows via urban rail modes during morning peak-hour) was developed using hierarchical cluster analysis for the case study of Istanbul Metropolitan City in Turkey since the rail investment is the major determinant in the definition of the network alternatives studied. Effects of the alternatives of Istanbul's 2023 Transport Master Plan networks on urban structure were modeled and compared using hierarchical cluster analyses (HCA). Analysis of the travel patterns over the alternative transport networks did not yield significant differences under the given constraint that the number of total trips in the metropolitan city was constant for all scenarios.
TopIntroduction
Types of urban transport investments have been long known by their impacts on the sustainability of transport and urban systems. With the increased share of public transport modes, the sustainability of a transport system increases since the cost (or travel time) of trip per passenger traveled decreases dramatically in the availability high-speed and high-capacity modes. Urban transport networks are generally invested to various degrees of public transit and highway infrastructures. In that respect, 2023 Istanbul’s master plan network alternatives had three alternatives developed in addition to the base scenario (existing and projects under construction with their projected termini by 2014 were counted). The 2023 network alternatives are defined based on their share of rail transit and highway projects, namely, i) rail-based, ii) highway-based, and iii) balanced or master plan scenario. The base network includes 29,861 km highway links (without the third Bosporus Bridge and its connections), and 231 km rail links. The rail-based network includes additional 357 km highway (without the third Bosporus Bridge and its connections) and 624 km rail links, the highway-based network includes additional 717 km highway (with the third Bosporus Bridge) and 343 km rail links, and the master plan network includes additional 717 km highway (with the third Bosporus Bridge) and 624 km rail links (ITMP, 2011).
The mode shares of the alternative future networks of Istanbul are tabulated in Table 1. It is seen that the highest share of public transit (48.77%) is achieved by the rail-based network. The second highest rate (48.04) belongs to the master plan network (ITMP, 2011). The master plan network includes the links of highway and rail systems included in the highway- and rail-based networks. The share of public transit in Istanbul is considered to be quite high and promising for sustainable transportation compared to developed countries where auto trips have the highest share of all trips. In addition, company and school shuttles can be considered as the modes of mass transportation. In that case, the share of mass transportation increases to 57.44% for the master plan network. For example, public transit constitutes 8.2%, 13.4%, 37.7%, 38.6%, 45.9%, 63%, 64.6% of motorized trips in Melbourne, Sidney, New York, London, Madrid, Seoul, Paris, respectively, in 2010-2011 (JOURNEYS, 2011).
Table 1. Mode shares of motorized trips for Istanbul’s alternative transport networks
| Networks | Trips by Auto (%) | Trips by Company and School Shuttles (%) | Trips by Public Transit (%) | Total No. of Motorized Trips | Trips per Capita | Trip Length (Auto/Transit)-min. | Trip Velocity (Auto/Transit)- km/h |
| Existing (2010) | 33.37 | 19.38 | 47.25 | 12,595,919 | 0.948 | 14.00/15.32 | N/A |
| Base (2023) | 42.92 | 9.37 | 47.71 | 25,907,698 | 1.505 | 25.00/26.52 | N/A |
| Rail-based (2023) | 42.02 | 9.21 | 48.77 | 25,907,698 | 1.512 | 24.55/24.76 | 19.15/19.03 |
| Highway-based (2023) | 42.78 | 9.44 | 47.78 | 25,907,698 | 1.507 | 23.89/25.02 | 19.40/19.12 |
| Master Plan (2023) | 42.55 | 9.40 | 48.04 | 25,907,698 | 1.509 | 23.85/24.75 | 19.74/19.63 |
Source: ITMP, 2011.
N/A: Not available.